1. Field of the Invention:
This invention relates in general to earth boring bits, particularly to those having rotatable cutters in which packing ring seals retain lubricant within the bearing areas.
2. Background Information:
One of the most successful seal means used in earth boring bits of the type having rotatable cutters is the O-ring seal. It successfully confines lubricant to the bearing area while excluding detritus for long periods of time before failure.
There are two general categories of O-ring seals utilized in earth boring bits: (1) those permitting axial motion or play of the O-ring; and (2) those utilizing a recess to retain the seal in one position relative to either the cutter or bearing shaft, usually the cutter.
Examples of those earth boring bits with seals permitting axial motion relative to the bearing shaft or cutter are U.S. Pat. Nos. 3,397,928; 4,014,595 and 4,516,641.
Examples of those seals which are confined in one position relative to the cutter are U.S. Pat. Nos. 3,765,495; 4,372,624; and 4,554,985.
The primary advantage of those O-ring seals permitting axial motion is the minimization of pressure pulses in the lubricant. Pressure pulses adjacent the seal can be detrimental and can result in leakage of lubricant or damage to the seal unless there is sufficient play of the seal in the recess to avoid extrusion. A sufficient amount of play reduces the magnitude of the pressure pulses to prevent extrusion of the O-ring from the seal recess (commonly called the "gland").
The advantages of those seals systems in which the seal is confined in one position, usually in the cutter, are: (1) protecting the seal from abrasives that cause wear and deterioration, 2) biasing the seal to keep the seal with the cutter to minimize pressure pulses and (3) preventing the pressure pulses in the lubricant from pushing the O-ring with excessive force against a stationary seal surface on the body of the bit.